Implantable cardiac devices are used to treat a patient's heart that does not function normally due to, for example, a genetic or acquired condition. A typical implantable cardiac device may perform one or more functions including sensing signals generated in the heart, pacing the heart to maintain regular contractions and providing defibrillation shocks to the heart.
Upon implant an implantable cardiac device is connected to one or more implantable cardiac leads. These cardiac leads are routed from the implanted cardiac device through the patient's body to the heart. Each cardiac lead includes one or more electrodes that are positioned adjacent to tissue at specific locations within the heart to enable sensing of cardiac signals or application of cardiac stimulation signals at those locations. For example, a typical implantable cardiac lead may include a bipolar electrode at its distal end for sensing cardiac signals and generating pacing signals and a coil electrode for generating shocking signals.
Various techniques have been used to implant a cardiac device and associated cardiac leads. An endocardial implantation technique generally involves gaining access to the interior of the heart via the venous return and implanting one or more leads within the heart. For example, an implantable device including circuitry for sensing signals from and generating stimulation signals for the heart may be subcutaneously implanted in the pectoral region of the patient. Leads connected to the device are routed from the device through a vein to the right side of the heart. A distal end of the lead is then passively or actively attached to an inner wall of the heart.
In practice, it may not be possible to position an electrode at a location that provides a desired level of sensing and pacing performance. For example, the implant location for an implantable cardiac lead depends on various factors such as the anatomy of the patient's venous system and the need to avoid incidental stimulation of the patient's anatomy. Here, factors such as a coronary sinus obstruction, the absence of a suitable cardiac vein for lead access, high threshold levels or potential phrenic nerve stimulation may prohibit the use of a traditional transvenous approach for the implantation of left ventricle leads in patients with cardiac heart failure (“CHF”) that are in need of cardiac resynchronization (“CRT”) therapy.
An epicardial implantation technique generally involves implanting leads at an outer layer of the heart (on the epicardium). Traditionally, this technique has been proposed for implanting coils across the heart to induce defibrillation shocks. Here, an implantable device including the defibrillation circuitry may be implanted in the abdominal region or the pectoral region of the patient. Sensing and stimulation leads are thus routed from the device to appropriate or preferred sites on the epicardium via an appropriate path.